Potential effects of regional pumpage on groundwater age distribution

Abstract

[1] Groundwater ages estimated from environmental tracers can help calibrate groundwater flow models. Groundwater age represents a mixture of traveltimes, with the distribution of ages determined by the detailed structure of the flow field, which can be prone to significant transient variability. Effects of pumping on age distribution were assessed using direct age simulation in a hypothetical layered aquifer system. A steady state predevelopment age distribution was computed first. A well field was then introduced, and pumpage caused leakage into the confined aquifer of older water from an overlying confining unit. Large changes in simulated groundwater ages occurred in both the aquifer and the confining unit at high pumping rates, and the effects propagated a substantial distance downgradient from the wells. The range and variance of ages contributing to the well increased substantially during pumping. The results suggest that the groundwater age distribution in developed aquifers may be affected by transient leakage from low-permeability material, such as confining units, under certain hydrogeologic conditions.

Age distributions and dynamically changing hydrologic systems: Exploring topography‐driven flow

“…The spatial and temporal distributions for the first moment of the AD ( a 1 ) are estimated from expressions (11). The first moment is a useful metric to evaluate the influence of transience on ADs and has been used to model the evolution of mean age during a pumping test in real fractured rock aquifers [e.g., Goode , ] and hypothetical unconfined and layered aquifer systems stressed by pumping [e.g., Zinn and Konikow , ]. A typical plot of mean age for steady flow can be found in Jiang et al .…”

Contribution of age data to the characterization of complex aquifers

“…Fundamentally, calibration capacity raises the issue of the sensitivity of groundwater ages to the aquifer properties and boundary conditions particularly in heterogeneous systems where neither the variability of properties nor their spatial distribution are well-characterized (Zinn and Konikow, 2007). In other terms, we are looking at the type of information effectively contained in groundwater ages.…”

Physical and Chemical Controls on the Simultaneous Occurrence of Young and Old Groundwater Inferred From Multiple Age Tracers

“…In doing so, we only considered a limited set of physical processes and combinations thereof. Also, the influence of transient pumping conditions on groundwater age discrepancies was also not closely investigated as it has been assessed in other studies (Engdahl, ; Zinn & Konikow, ; Zuber et al, ). Nevertheless, the study provides a comprehensive assessment of field conditions that can lead to discrepant ages as reported by multiple environmental tracers and the limit to which physical processes alone can explain the often‐observed discrepancies.…”